The present invention generally relates to a starter to be used, for example, in an internal combustion engine, and particularly, to a starter provided with a dust cover for protecting dust-proof and water-proof sealing parts disposed in the starter.
In a starter, generally, a magnetic switch is actuated to drive a shift lever to thereby make a pinion and a ring gear engage with each other. With this type of starter, the magnetic switch and a motor are mounted so as to close an open end formed in a front case with the axes of both the magnetic switch and the motor substantially parallel to each other. When assembled, the motor and magnetic switch close an open end of the front case except for a gap between the magnetic switch and the motor. A dust cover, which acts as a seal member, is attached to prevent dust and water from entering the inside of the front case through the gap.
Generally, the starter is assembled as follows. First, a pinion, a shift lever and a part of the motor are mounted in the front case. Next, a dust cover is attached. Finally, the magnetic switch and the body of the motor are attached. The dust cover is typically comprised of, for example, synthetic resin. The dust cover is fitted and fixed in the front case (or an intermediate member fixed in the front case which is hereinafter merely referred to as "intermediate member") in parallel with the longitudinal axis of the motor. Examples of this type of structure am described, for example, in JP-B 63-1459, and JP-A 63-16168.
In this configuration, the dust cover fits in the front case (or an intermediate member thereof) in parallel with the longitudinal axis of the motor as described in the above references. However, several problems arise from this configuration.
In order to seal the starter, it is desirable to make the outer size of the dust cover considerably larger than the size of a hollow in the front case (or an intermediate member) into which the dust cover fits. The difference in size increases the interference between the dust cover and the hollow so that the dust cover can be pushed and expanded into the hollow. If the interference is too large, however, the dust cover must be greatly deformed when the dust cover is fitted, so that assembly is difficult.
Alternatively, to ease assembly, it is desirable to make the outer size of the dust cover and the inner size of a hollow of the front case (or an intermediate member), into which the dust cover is to be fitted, agree with each other as well as possible. When the sizes are similar, the interference is small, so that the dust cover need only be marginally deformed when assembled. However, with less interference between the members, the dust cover is not expanded into the hollow to completely seal the staffer. Large interference between the parts is necessary to affect the seal between the dust cover and the case. Accordingly, the ease of assembly and the integrity of the seal are incompatible considerations. It is impossible to both easily assemble the dust cover into the front case and create a good seal.
Further, in order to ease assembly, a taper is formed in a hollow of the front case (or intermediate member) in parallel with the longitudinal axis of the motor so that the width of the hollow decreases in the fitting direction. The taper in the hollow of the front case (or intermediate member) makes it easier to assemble the dust cover. However, in order to create a dependable seal between the dust cover and the front case, it is necessary to increase the interference between the member because there is no means to push the back of the dust cover in the direction along which the taper becomes narrower, i.e., in the direction parallel to the longitudinal axis of the motor. Therefore, because the interference must be increased, the net affect of the taper is that ease of assembly is not improved.